This invention relates to an electromagnetic pump of the type utilized to feed fuel to an engine of a motor car.
As disclosed in U.S. Pat. No. 3,400,663 the electromagnetic pump of this type comprises a U shaped housing member, a cylindrical bobbin wound with an exciting coil and disposed in a space in the housing member, a cylindrical nonmagnetic sleeve disposed in the central opening of the bobbin and slidably containing a magnetic plunger, inlet and outlet fixtures threaded to the housing member for holding the opposite ends of the sleeve and a return spring contained by the sleeve for applying return bias to the plunger. The magnetic flux created by pulsating current flowing through the exciting coil cooperates with the return spring to reciprocate the plunger so as to pump liquid from an inlet passage in the inlet fixture to a discharge passage of the outlet fixture through an inlet valve and an outlet valve.
The opposite ends of the sleeve of this pump are fitted in cylindrical portions of the inlet and outlet fixtures respectively. Leakage of the liquid through the joints between the sleeve and the inlet and outlet fixtures is prevented by soldering the outer surface of the sleeve to the end of the outlet fixture and by providing an O-ring in an annular groove on the inner surface of the cylindrical portion of the inlet fixture for sealing the contacting surfaces of the inlet fixture and the sleeve member.
With this construction, however, in order to make uniform the clamping force of the O-ring against the sleeve it is necessary to precisely machine the annular groove.
Moreover, soldering of the outlet fixture and the sleeve is troublesome and if they become eccentric during the soldering operation or if they are secured together in a bent state, the sleeve will be deforemd by the inlet fixture when they are incorporated into the housing member thus making it impossible to assure smooth motion of the plunger. This also renders nonuniform the clamping force of the O-ring which prevents the establishment of a good seat.
When threading the inlet and outlet fixtures into the housing member, if the screw threads of the inlet and outlet fixtures are not in correct coaxial relationship the inlet and outlet fixtures will be secured noncoaxially thus causing deformation of the sleeve and impaired movement of the plunger.
Accordingly, in such prior art electromagnetic pumps it is necessary to machine the component parts to high accuracies. In addition, assembling of the component parts is troublesome, thus increasing the cost.